1. Field of the Invention
The present invention relates to a disk apparatus having an optical pickup, and more particularly, to an apparatus having an optical pickup whose movement in the direction of the radius of the disk is required to be guided with high accuracy by a guide shaft that is circular in cross section.
2. Description of the Related Art
FIG. 8 is a schematic plan view showing the general structure of an optical pickup attached part of this type of disk apparatus. In the figure, reference numeral 1 denotes a chassis, and a turntable 2 fixed to the rotation shaft of a non-illustrated driving motor is disposed in a predetermined position of the chassis 1. The chassis 1 has an opening 3, and in an inner area of the opening 3, an optical pickup 10 is moved in a far and near direction with respect to the turntable 2, that is, in the direction of the radius of a disk D rotated by the turntable 2 (the direction of the arrow R). The motor serving as a movement driving source for moving the optical pickup 10 is not shown.
The optical pickup 10 is formed by mounting, on a base 20 formed of a synthetic resin molding, an optical system that has an objective lens 12 and a non-illustrated optical axis adjusting mechanism and scans a disk. The base 20 is provided with a bearing 30 including a pair of front and rear bearing elements 31 and 32 provided on one side and in the lateral direction and an engagement portion 40 provided on the other side end in the lateral direction, the bearing 30 is swingably supported by a guide shaft 50, and the engagement portion 40 is guided by a guide rail 60 disposed parallel to the guide shaft 50.
It is found that in such an optical pickup 10, the position of engagement between the guide rail 60 and the engagement portion 40 is not required of a high accuracy demanded for the engagement portion 40 to be guided by the guide rail 60 without any backlash although the bearing 30 is required to be guided by the guide shaft 50 with high accuracy without any backlash. For this reason, as shown in the schematic perspective view of FIG. 9, the engagement portion 40 has a pair of protruding pieces 41 and 42 slidably sandwiching, in the longitudinal direction, the guide rail 60 including a round bar that is circular in cross section, and play S in which the engagement portion 40 is displaceable in the lateral direction with respect to the guide rail 60 is frequently secured between the protruding pieces 41 and 42.
Under such conditions, an optical pickup of a conventional disk apparatus will be described with reference to FIG. 10 through FIG. 12. FIG. 10 is a schematic bottom view showing a relevant part of the optical pickup for which the part is viewed from the underside. FIG. 11 is a schematic cross-sectional view taken on the line XI—XI of FIG. 10. FIG. 12 is an enlarged view on the arrow XII of FIG. 10.
In this optical pickup, the pair of front and rear bearing elements 31 and 32 of the bearing 30 provided on one side end, in the lateral direction, of the base 20 formed of a synthetic resin molding have round holes 33 and 34, and cylindrical sliding surfaces 35 and 36 including the inner circumferential surfaces of the round holes 33 and 34 are slidably in contact with the guide shaft 50 that is circular in cross section (see FIG. 8) with high accuracy without any backlash. In FIG. 10 and FIG. 12, reference numeral 21 denotes a rack to which the output of a non-illustrated motor is transmitted. In the optical pickup shown in FIG. 10 through FIG. 12, an engagement portion provided on the other side end, in the lateral direction, of the base 20 has a structure similar to that of the engagement portion 40 described with reference to FIG. 8, and is slidably engaged with the guide rail 60 described with reference to FIG. 8 with a similar structure. The other structures are similar to those described with reference to FIG. 8.
In the conventional disk apparatus having such an optical pickup 10, when the base 20 integrally provided with the bearing 30 is molded of a synthetic resin, since the front and rear bearing elements 31 and 32 constituting the bearing 30 have the round holes 33 and 34, a metal mold slide pin 70 for molding shown by alternate long and short dashed lines in FIG. 10 is used. Since the metal mold slide pin 70 elongates from a non-illustrated metal mold main part and a single metal mold slide pin 70 is used for forming both the round holes 33 and 34 of the front and rear bearing elements 31 and 32, it is necessary that the metal mold slide pin 70 elongating from the metal mold main part be long enough to form both of the round holes 33 and 34 of the front and rear bearing elements 31 and 32, and further, the mold releasing stroke when the metal mold slide pin 70 is taken out in the direction of the arrow A of FIG. 10 at the time of mold releasing after molding is long.
On the contrary, in the conventional apparatus having the optical pickup 10, the engagement portion having a similar structure to the engagement portion 40 described with reference to FIG. 8 or 9 can be molded by use of a general-purpose split-cavity mold moved toward a side of the base 20 for mold releasing without the use of the above-mentioned metal mold slide pin 70, because it has the pair of upper and lower protruding pieces 41 and 42 and the space between the protruding pieces 41 and 42 is open toward the side of the optical pickup.
On the contrary, a prior art example describes a disk drive apparatus having an optical pickup where a bearing including two front and rear bearing elements is slidably supported by a main guide shaft (corresponding to the above-mentioned guide shaft) and an engagement portion guided by a round-bar-shaped sub guide shaft (corresponding to the above-mentioned guide rail) disposed parallel to the guide shaft is provided (for example, see JP-A-2001-222823). The structure of this disk drive apparatus is similar to that of the above-mentioned conventional example in that the main guide shaft is inserted in round holes of the front and rear bearing elements and the engagement portion has protruding pieces that sandwich the sub guide shaft in the longitudinal direction.
Another prior art example mentions an optical pickup bearing mechanism where a first bearing portion (corresponding to the above-mentioned bearing) is slidably supported by a first guide rod (corresponding to the above-mentioned guide shaft) and a second bearing portion (corresponding to the above-mentioned engagement portion) is guided by a second guide rod (corresponding to the above-mentioned guide rail) (for example, see JP-A-2003-77234). This example describes, as the structure of the second bearing not required of very high accuracy, that the second guide rod is slidably sandwiched, in the longitudinal direction by use of spring tension, between a first sliding portion on the side of the optical pickup base and a second sliding portion on the side of a holder attached to the optical pickup base.
Still another prior art example mentions a guide mechanism where two front and rear U-shaped holders are provided on one side end of a base on which a magnetic head is mounted, and a cylindrical bearing in which a guide rod is slidably inserted is held by these holders (for example, see JP-A-61-175712).
When a structure where the round holes 33 and 34 are provided in the front and rear bearing elements 31 and 32 of the bearing 30 and the guide shaft 50 is inserted in the round holes 33 and 34 is adopted in order to satisfy the demand for guiding the bearing 30 by the guide shaft 50 with high accuracy without any backlash like the optical pickup of the conventional disk apparatus described with reference to FIG. 10 through FIG. 12, it is required to use an elongate metal mold slide pin 70 as the forming die for the round holes 33 and 34 as described with reference to FIG. 10.
However, when such an elongate metal mold slide pin 70 is used, the overall size of the molding machine for molding the base 20 is increased in accordance with the length of the metal mold slide pin 70 and the number of necessary metal mold parts is increased, so that although the engagement portion 40 (see FIG. 9) can be molded by use of a general-purpose split-cavity mold, the cost of the metal mold is increased, so that the cost of molding the base 20 is increased. Moreover, the elongate metal mold slide pin 70 readily deforms or breaks because of being long and further, the cost required for replacing the metal mold slide pin 70 is high.
Moreover, the sliding surfaces 35 and 36 including the inner circumferential surfaces of the round holes 33 and 34 of the front and rear bearing elements 31 and 32 are straight in the direction of the axis line of the metal mold slide pin 70 because they are molded by the metal mold slide pin 70, so that the area of contact with the guide shaft is large and this can increase the load on the motor for driving the optical pickup.
The disk drive apparatus described in JP-A-2001-222823 has a similar problem as the conventional example because the optical pickup thereof has the structure where the bearing having round holes is slidably supported by the main guide shaft and the engagement portion having upper and lower protruding pieces is slidably engaged with the sub guide shaft. Moreover, the art described in JP-A-2003-77234 cannot be a solution to the above-mentioned problem because it merely provides a structure of the second bearing portion not required of very high accuracy. Further, the mechanism described in JP-A-61-175712 cannot be a solution to the above-mentioned problem, either, because it has the structure where the cylindrical bearing in which the guide rod is slidably inserted is held by the U-shaped holders.